Shank drill

ABSTRACT

A shank cutter has plural circumferential cutting edges which run in a helical manner in the region of its cutting section and of which at least one critical number are equipped in each case with a preferably essentially flattened roughing profile with chip-separating grooves with rounded bases, so that the chip-separating grooves of cutter ridges which are adjacent in the circumferential direction are axially offset relative to each other. To create a tool which provides long service life by combined advantages of a vibration-stabilized finishing cutter and a conventional roughing cutter, at least one circumferential cutting edge has an angle of twist which differs from that of another circumferential cutting edge. In addition, the chip-separating grooves of the circumferential cuffing edges which are equipped with a roughing profile in each case merge into a preferably essentially flattened central section of the roughing profile by means of a predefined flank radius.

FIELD OF THE INVENTION

The invention relates to a shank cutter according to the preamble ofpatent claim 1.

BACKGROUND OF THE INVENTION

Such cutters have as a common feature a shank as the chucking part,which is inserted into the tool holder. Such cutters are used forexample as slotting cutters or die-sinking cutters with a flat or roundend. Such cutters are furthermore characterised in that they have aplurality of circumferential cutting edges in the region of theircutting section on the cutter ridges which are separated from each otherby flutes, which cutting edges run in a helical manner and are in eachcase configured with a roughing profile in such a manner that thecircumferential cutting edges are given chip-separating grooves, withthe chip-separating grooves of cutter ridges which are adjacent in thecircumferential direction being axially offset with respect to eachother.

Such roughing profiles are standardised in “round” and “flat” versionsfor example in DIN 1836, with a differentiation being made between“extra coarse”, “coarse” and “fine” with regard to the structure of theprofile, where applicable with regard to the pitch with which thechip-separating grooves are introduced into the cutter ridges. Theprofile structure such as also these pitches of the recesses which formthe chip-separating grooves, depends on the tool, with the pitch beingselected to be finer with increasing hardness of the material to bemachined. The pitch can furthermore be dependent on the tool diameter,with it being the case here that the smaller the diameter of the shankcutter, the finer the pitch.

In contrast to finishing cutters, which usually have no profiling of thecutting edge or face, the interrupted, that is, profiled profile of thetool cutting edge of the roughing cutter allows a more rapid breaking ofthe chip. The roughing cutter is however generally not suitable for theproduction of a uniform surface with a high surface quality. Owing tothe short-chipping behaviour of the removed material, however, muchbetter chip removal is produced than with the finishing cutter. Owing tothe high material removal rate, roughing tools of the type mentioned atthe start are also very suitable for work in which it is a matter ofremoving material as effectively and quickly as possible to a finishinglevel of for example 0.5 mm before a work step with a finishing tool.Also, the cutting pressure and the power consumption of the machine arelower when working with such roughing cutters, and the tool can producea high cutting depth and cutting width.

On the other hand, finishing cutters, that is, shank cutters with smoothcutting edges, can produce a workpiece surface with high dimensionalaccuracy and quality, that is, smoothness, which is produced owing tothe regularity of the tool cutting edge, the high speed with at the sametime low feed rate of the cutting tool and the generally low chip volumeowing to the low finishing level, which can be between 0.1 and 1.0 mmdepending on the application. If such finishing tools are however usedwith greater cutting depths or widths, chip removal problems occur owingto the longer and larger chips and also the power consumption and thecutting pressure increase over-proportionately. In order to reduce thetendency to vibrate which arises thereby, the cutting edge geometry hasbeen changed—as described for example in the document DE 37 06 282 C2—byworking with at least two unequal angles of twist in the region of thecircumferential cutting edges, that is, the main cutter edges.

These unequal angles of twist mean that vibrations of the cutting toolcan be minimised, which can be used to increase the service life orconversely to increase the feed rate values. Owing to the comparativelyhigh power consumption and the high cutting pressure as well as thecritical chip removal as before, this known finishing cutter can alsoonly be operated at relatively small cutting widths.

SUMMARY OF THE INVENTION

The invention is therefore based on the object of developing a shankcutter of the type described at the start, in particular according tothe preamble of patent claim 1 in such a manner that it is in particularsuitable for providing a high material removal rate and at the same timemachining the workpiece with good surface quality while ensuring hightool life travel, low power consumption of the machine and reducedcutting pressure.

This object is achieved by the features of patent claim 1.

According to the invention, the measure of varying the angle of twist ofthe circumferential cutting edges which are at a circumferentialdistance from each other, which is known from the field of finishingcutters, is combined with a new geometry of the chip-separating grooves,as a result of which a cutting tool is produced which combines only theadvantages of conventional roughing and finishing cutters with regard tochip formation, power consumption of the machine, cutting pressure, chipremoval, the cutting width which can be achieved and the surfacequality.

The shank cutter according to the invention produces short chips asbefore and therefore has a low power consumption. Furthermore, thecutting pressure is low, and good chip removal is produced owing to theshort chips. Owing to the flattened roughing profile in connection withthe measure of at least two circumferential cutting edges havingdifferent angles of twist, the tendency to vibrate of the cutter, whichis normally pronounced because of the roughing profile, is considerablyreduced, so that very high quality surfaces with a good tool life travelcan be produced over the preferably essentially flattened regions of theroughing profile or with a roughing/finishing profile to DIN 1836, sincethe rounded portions of the chip-separating grooves in the transition tothe preferably essentially flattened section of the roughing profileeffectively ensure soft cutting with minimised impact loading of thecircumferential cutting edges over the service life of the tool. Thecutting tool according to the invention is in this manner particularlysuitable for working with high cutting widths and depths, for examplewhen cutting grooves, with the chip shape remaining as favourable aswith pure rough-machining.

Advantageous developments of the invention are the subject of thedependent claims.

The shank cutter can in principle be equipped with any number ofcircumferential cutting edges. With more than three circumferentialcutting edges or cutter ridges, it is advantageous according to claim 2to form the angles of twist of adjacent circumferential cutting edgesdifferently in each case.

If an even number of circumferential cutting edges is provided, it isadvantageous from a production standpoint to equip in each case twodiametrically opposite circumferential cutting edges with the same angleof twist.

The different angles of twist of the circumferential cutting edges atthe same time means that what is known as the pitch of the shank cutter,that is, the distribution of the circumferential cutting edges as seenin radial section, changes in the axial direction. It is advantageousaccording to claim 4 to keep the pitch of the cutter equal in a radialplane which lies in the cutting section, in particular if the shankcutter is equipped with a cutting section of considerable axial lengthand the differences in the angles of twist are comparatively great. Itis however equally possible to place this radial plane outside thecutting section, especially if the shank cutter according to theinvention in any case produces very short chips and therefore is to beconsidered much less critical than a conventional finishing cutter withregard to chip removal.

It has been found that differences in the angle of twist in the rangefrom 1 to 6° lead to particularly favourable chipping behaviour of theshank cutter, with it being possible for the value to depend on thematerial to be chipped and/or on the material of the shank cutter and/oron its coating.

Experiments have furthermore shown that it is advantageous to set theflank radius over which the chip-separating groove merges into theflattened section of the roughing profile in the range from 0.1 to 1.0mm, particularly preferably from 0.1 to 0.5 mm, in order to maintain therequired service life and specified surface quality.

Various production methods come into consideration for producing thechip-separating grooves. For example, it is possible to grind thechip-separating grooves into the circumferential cutting edges by meansof a profile-grinding disc. According to one embodiment, thechip-separating grooves are angled towards a plane of the shank cutterwhich is perpendicular to a longitudinal axis of the shank cutter, as aresult of which it is possible to influence chip formation in anadvantageous manner. In this case the chip-separating grooves can ineach case in sections follow the course of a helix, the lead of whichcorresponds to the pitch of the roughing profile or to a whole multipleof the pitch.

It is however equally possible to form the chip-separating groovesparallel to a plane of the shank cutter which is perpendicular to alongitudinal axis of the shank cutter.

According to a further advantageous configuration, the flank radius,which in each case faces the cutter shank is smaller in thechip-separating groove than the other flank radius, in particular in thecase where the flank radius which faces the cutter shank firstcontributes to chip formation. With this measure, the service life ofthe shank cutter can be further increased, with it being possible at thesame time for the vibration tendency to be reduced and the quality ofthe surface which can be produced thereby to be improved.

The chipping output, the surface quality and the service life of thetool can be further optimised by the choice of the material of the shankcutter. It has been found that the design according to the inventionreveals its particular advantages if the tool as a whole or at least inthe region of the cutting section is produced from a hard material, withfor example solid hard metal, but also a cermet material being used asthe hard material.

Depending on the field of use of the shank cutter, that is, depending onthe chipping task, in particular depending on the material to bechipped, it can be advantageous to provide an internal coolant/lubricantsupply system and/or a suitable coating. All customary hard materialcoatings, but also soft material coatings can be considered as coatings.In this regard, reference is made by way of example to the coatingsdescribed in the applicant's manual: “Gühring—Wer bietet mehr?[Gühring—Who offers more?]—German edition 2006, price list No. 40, onpages 1426 as “A layer or TiAlN layer”, as “Super A layer”, “C layer orTiCN layer”, as “F layer”, as “P layer (AlCrN layer)”, as “S layer” or“TiN layer” or as “M layer based on MoS2”.

BRIEF DESCRIPTION OF THE DRAWINGS

A plurality of exemplary embodiments of the invention are described inmore detail below with the aid of schematic drawings. In the figures,

FIG. 1 shows a schematic side view of the shank cutter with fourcircumferential cutting edges;

FIG. 1A shows detail “IA” in FIG. 1 in an enlarged illustration;

FIG. 2 shows a section of the roughing profile according to theinvention in an enlarged illustration;

FIG. 3 shows a side view of the shank cutter in order to illustrate theposition of the cross section on which the circumferential cutting edgesare arranged with the same angular distance from each other;

FIG. 4 shows the end view of the tool according to FIG. 3, looking alongthe arrow “IV”;

FIG. 5 shows the section according to V-V in FIG. 3 in an enlargedillustration;

FIG. 6 shows a schematic winding of the shank cutter according to FIG.3;

FIG. 7 shows a perspective side view of the shank cutter according tothe invention;

FIG. 8 shows the end view of a modified embodiment of the shank cutter,in which equal pitch is present on the end face;

FIG. 9 shows a detailed view of a circumferential surface of a modifiedexemplary embodiment of the shank cutter;

FIG. 10 shows a schematic diagram to illustrate the chip formation ofadjacent circumferential cutting edges; and

FIG. 11 shows a modified roughing profile in an enlarged illustration.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, a shank cutter is referred to with the reference symbol 20and has a cutting section 22 and a clamping shank 24. The cutter axis isreferred to with 21. In the example shown, both the cutting section andthe clamping shank have a cylindrical configuration. The cutting sectioncan however equally have a different envelope, for example an envelopein the shape of a cone surface.

The line 26 indicates that the shank cutter has what is known as a neckcountersink, that is, the outer diameter of the clamping shank 24 isslightly bigger than the nominal diameter of the cutting section 22.

The cutting section 22 has a plurality of circumferential cutting edges26-1 to 26-n, which run in a helical manner and between which flutes28-1 to 28-n are formed. In this shank cutter the circumferentialcutting edges are the main cutting edges. At the end face is formed anumber of auxiliary cutting edges which corresponds to the number ofcircumferential cutting edges in a conventional manner so that a moredetailed description of this geometry can be omitted here.

As can be seen in detail in FIG. 1A, the individual circumferentialcutting edges are in the exemplary embodiment shown in each caseequipped with a flattened roughing profile 30 which is formed bychip-separating grooves 32 and a flattened section 34 which lies betweenthem. A central section can also be present instead of the flattenedsection, which central section follows a preferably slightly convex lineas viewed in the longitudinal section of the cutter. The chip-separatinggrooves 32 extend in the exemplary embodiment shown over the entirewidth of the cutter ridges, which are referred to with 36-1 to 36-n, insuch a manner that the chip-separating grooves of cutter ridges 26-1 and26-2, 26-2 and 26-3, 26-n and 26-1 which are adjacent in thecircumferential direction are axially offset with respect to each otherso that the parts of material which are not cut by a circumferentialcutting edge can be removed by the next cutting edge. The chippingthickness is in this manner doubled, so that according to Kienzle andVictor's machining principle the specific cutting force is reduced andthe torque and the power consumption are less than with tools with acontinuous circumferential cutting edge, that is, in finishing cutters.

FIG. 2 shows schematically and on a greatly enlarged scale how theroughing profile 30 is equipped in detail in the shank cutter accordingto the invention. The individual chip-separating grooves 32 have arounded groove base 40 with an extremely small radius R40. Thechip-separating groove 32 merges into the flattened section 34 by meansof a first flank radius RF1. The flank radius RF1 is on the side of thechip-separating groove 32 which faces away from the cutter shank 24. Onthe side which faces the cutter shank 24, the respective chip-separatinggroove 32 merges into the flattened section 34 of the roughing profileby means of a second flank radius RF2. The pitch of the roughingprofile, that is, the axial distance between chip-separating grooves 32of a circumferential cutting edge, is referred to with T and the depthof the roughing profile 30 is referred to with H.

The values RF1, RF2, T and H, and thus also the axial dimension A34 ofthe flattened section 34 are variable in order to carry out anadaptation to the chipping conditions, that is, to the material to bechipped, to the cutting speed and to the material removal rate. It hasbeen found, however, that the following conditions are of particularadvantage:

1. The flank radius RF1 and RF2 should be in the range from 0.1 to 1 mm,particularly preferably from 0.1 to 0.5 mm;

2. The size of the smallest radius RF40 in the base 40 of thechip-separating groove 32 should be greater than the flank radius RF1 orRF2;

3. The flank radius RF2, which leads during cutting in the direction ofrotation, that is, in the cutting direction, of the shank cutter whichhas a right-handed twist in the embodiment according to FIG. 1, that is,the flank radius RF2, which faces the cutter shank, of thechip-separating groove, should be greater than the flank radius RF1which faces away from the cutter shank. In other words, the flank radiuswhich first does the cutting work when the roughing profile penetratesthe workpiece should be greater than the other flank radius.

With this measure it is possible to keep the service life of the cuttingedges and the surface quality of the machined workpiece surface at avery high level.

A further special feature of the shank cutter according to the inventioncan be seen in that the angle of twist, which referred to with θ1 to θn,of the circumferential cutting edges 26-1 to 26-n are different fromeach other, as follows:

In the most general case, at least one angle of twist θ differs fromanother angle of twist θ of the circumferential cutting edges.

According to an advantageous development, the angles of twist at leastof adjacent circumferential cutting edges differ from each other.

In the embodiment of the shank cutter which is shown in the drawings, aneven number of circumferential cutting edges 26-1 to 26-4 is provided,with in each case two diametrically opposite circumferential cuttingedges 26-1 and 26-3, 26-2 and 26-4 having the same angle of twist θ.This can be seen best in FIG. 3. The circumferential cutting edge 26-1on the cutter ridge 36-1 has for example an angle of twist θ1, whichdiffers from the angle of twist θ2 of the adjacent circumferentialcutting edge 26-2 by 1° to 6°, preferably by 1° to 3°. The angle oftwist of the circumferential cutting edge 26-1 corresponds exactly tothat of the circumferential cutting edge 26-3, and the angle of twist ofthe circumferential cutting edge 26-2 corresponds exactly to that of thecircumferential cutting edge 26-4. The angle of twist θ can vary withinwide limits and be for example in the range from 20° to over 50°,depending on the chipping task present in each case.

Using the winding according to FIG. 6, it can be explained how the pitchof the shank cutter changes owing to these differing angles of twist. Itis assumed that the radial plane in which the cutter has an equal pitchis situated at a predefined distance AGT from the cutter end 50, thatis, at which the circumferential distance of the circumferential cuttingedges from each other is equal. In other words, the respective centralangle between the adjacent circumferential cutting edges is 90°.

Furthermore, if the angles of twist of circumferential cutting edges26-1 and 26-3, 26-2 and 26-4 which lie diametrically opposite each otherare equal but of different sizes, namely have the angle of twist θ1 orθ2, an unequal pitch is produced on the end face of the shank cutter—asshown in FIG. 4. In other words, the central angle between the adjacentcircumferential cutting edges 26-1 and 26-2, 26-3 and 26-4 is less than90°, whereas the other central angle is more than 90°.

The plane of section V-V in FIG. 3 is thus placed such that its axialdistance from the cutter end corresponds to the dimension AGT. There istherefore an unequal pitch in all the other sectional planesperpendicular to the cutter axis 21.

It has been found to be advantageous if the dimension AGT isapproximately 30% of the length L22 of the cutting section 22. It ishowever possible—depending on the field of application and use of theshank cutter and on the difference between the individual angles oftwist θ1 to θn—to vary the dimension AGT within wide limits. It can evenbe possible, with a correspondingly small difference between theindividual angles of twist of different or adjacent circumferentialcutting edges, to make the dimension AGT greater than the dimension L22,and even to set it to be negative, that is, to place the radial plane ofequal pitch outside the cutting section 22.

FIG. 7 shows a perspective view of a shank cutter which has been testedin use. It can be seen in this figure that the chip-separating grooves32 are introduced, preferably ground, in such a manner that they areslightly angled towards a plane, which is perpendicular to the cutteraxis 21, of the shank cutter. This shape can be realised in that aprofiled grinding disc is used to grind the chip-separating grooves,which grinding disc has a profile corresponding to the detail drawingaccording to FIG. 2, that is, an outer contour with the radii R40, RF1and RF2. This grinding disc can be angled towards the plane, which isperpendicular to the cutter axis 21, of the shank cutter at a predefinedangle, so that the profiled grinding disc can move along a helix, thelead of which corresponds to the pitch T of the roughing profile 30 withthe chip-separating grooves 32.

Modified embodiments are shown in the other figures. In this case thecomponents which correspond to the constituent parts of theabove-described cutter are provided with similar reference symbols, butwith a “1”, “2” or “3” in front.

FIG. 8 schematically shows the end view of a modified embodiment of theshank cutter. In this variant the arrangement is such that an equalpitch of the circumferential cutting edges 126-1 to 126-4 is present onthe cutter end. In other words, the plane of section V-V in FIG. 3 is atthe cutter end in this variant.

FIG. 9 shows a modified embodiment of the shank cutter, in which thechip-separating grooves which are referred to with 232 are orientedslightly differently than in the above-described exemplary embodiment.As can be seen in FIG. 9, the chip-separating grooves 232 run parallelto a normal plane to the cutter axis 221. The dashed line 254 indicatesthat chip-separating grooves are offset by a dimension V by cutterridges 236-1 and 236-2 which are adjacent in the circumferentialdirection, where:

V=T/n,

where T means the pitch of the roughing profile (cf. FIG. 2) and n meansthe number of circumferential cutting edges 226-1 to 226-n.

The above-described structure produces a shank cutter which is suitablein particular for machining materials which are difficult to chip whileproviding large cutting widths, that is, a shank cutter in particularfor cutting flanks, grooves, diagonal drill holes or spiral shapes. Itis indicated using FIG. 10 how chip formation takes place with the shankcutter according to the invention. VPU refers to the feed rate perrevolution of the shank cutter. T is the pitch of the roughing profile.V1 to V4 refer to the axial offset of the circumferential cutting edgeswhich are adjacent to flattened sections 34 of the roughing profile. Theequal or unequal pitch of the circumferential cutting edges (cf. FIG. 6)which is present in the respective axial plane defines the sequence inwhich the teeth of the relevant roughing profile of the circumferentialcutting edges are engaged and how the chipping thickness changes. Forexample, the size of the chipping thickness DS1 is slightly less thanthe size of the subsequent chipping thicknesses DS2 if thecircumferential distance between the circumferential cutting edges whichare engaged one after the other is greater than the previouscircumferential distance.

It is apparent from this illustration that these multiple irregularitiesin chip formation, which change again over the axial length of the shankcutter, counteract the risk of tool instability caused byself-oscillation. The shank cutter according to the invention thereforenot only operates at an optimum material removal rate, but also in sucha manner that a very good workpiece surface can be realised even withlarge cutting widths and a good service life.

This advantageous effect can be enhanced further by suitable materialchoice in the structure of the shank cutter. According to anadvantageous development, the whole shank cutter consists of a hardmaterial, in particular from solid hard metal, as a result of whichimproved rigidity and an even lower susceptibility to vibration isproduced. The service life of the shank cutter can be further optimisedby suitable coatings.

The geometry of the roughing profile, in particular the ratio of thepitch to the axial length of the flattened section and/or the ratio ofthe pitch to the depth of the chip-separating groove is preferablyselected as a function of the physical characteristics of the materialto be chipped.

In all the above-described embodiments, the roughing profile is equippedwith a completely flattened central section 34. This geometry is howevernot absolutely necessary to achieve the advantages according to theinvention to a critical extent. The central section can also be rounded,preferably slightly bulged or convex, which will be explained in moredetail below using FIG. 11.

In this roughing profile 330 too, the individual chip-separating grooves332 have a rounded groove base 340 with an extremely small groove radiusRN. The chip-separating groove 332 merges into a slightly convex butstill essentially flattened central section 334 by means of a firstflank radius RF1. The flank radius RF1 is on the side of thechip-separating groove 332 which faces away from the cutter shank. Onthe side which faces the cutter shank, the respective chip-separatinggroove 332 merges into the central section 334 of the roughing profileby means of a second flank radius RF2. The pitch of the roughingprofile, that is, the axial distance between adjacent chip-separatinggrooves 332 of a circumferential cutting edge, is again referred to withT and the depth of the roughing profile 30 is referred to with H.

The values RF1, RF2, T and H, and thus also the axial dimension LB ofthe essentially flattened but convex section 334 are again variable inorder to carry out an adaptation to the chipping conditions, that is, tothe material to be chipped, to the cutting speed and to the materialremoval rate. The following also applies with this embodiment:

1. The flank radius RF1 and RF2 should be in the range from 0.1 to 1 mm;2. The size of the smallest radius RN in the base 340 of thechip-separating groove 332 should be greater than the flank radius RF1or RF2;3. The flank radius RF2, which leads during cutting in the direction ofrotation, that is, in the cutting direction, of the shank cutter whichhas a right-handed twist in the embodiment according to FIG. 1, that is,the flank radius RF2, which faces the cutter shank, of thechip-separating groove, should be greater than the flank radius RF1which faces away from the cutter shank. In other words, the flank radiuswhich first does the cutting work when the roughing profile penetratesthe workpiece should be greater than the other flank radius.

In the exemplary embodiment of FIG. 11, the contour of the roughingprofile can be formed by four circular line sections. The section withRF1 is connected to the section with RN, to this the section with RF2and to this the section with the radius RK, which can be in the regionof the size of the groove radius RN but also bigger than this,preferably by a multiple. The central section 334 can also—differingfrom a circular line—be formed by another curve.

The convexity K of the profile is preferably low in the region of thecentral section 334. The following preferably applies, with reference toFIG. 11:

K:LB 0.5, particularly preferably

K:LB 0.05.

where the dimension LB refers to the profile length between the flankradii RF1 and RF2.

Of course, deviations from the described exemplary embodiment arepossible without departing from the basic idea of the invention.

The cutting part can for example be configured with other, conventionalcutting edge geometries.

It is also possible to equip the tool with an internal coolant/lubricantsupply system.

Furthermore, the angle of twist of the individual circumferentialcutting edges can change either continuously or discontinuously over theaxial length of the shank cutter.

Cutting inserts can also be used instead of cutting edges which areformed in one piece with the shank cutter material.

It is furthermore possible to change the end geometry of the cutterwithin wide limits. The cutting parts can be configured to berectangular, with corner chamfer or ball end.

The roughing profile can also have an unequal pitch in the individualcircumferential cutting edges, that is, irregularly over the axiallength. It is also possible to change the cross section of thechip-separating grooves in the circumferential direction.

Finally, a different profile can be formed on the different cutterridges. It is also possible to expose individual circumferential cuttingedges or diametrical pairs of cutting edges of the circumferentialcutting edges. In other words: A modification can be made in such amanner that, in the case of 4 circumferential cutting edges, cuttingedges 1 and 3 are equipped with a roughing profile, whereas cuttingedges 2 and 4 are smooth.

The invention thus creates a shank cutter which has a plurality ofcircumferential cutting edges which run in a helical manner in theregion of its cutting section and of which at least one critical numberare equipped in each case with a preferably essentially flattenedroughing profile with chip-separating grooves with rounded bases, insuch a manner that the chip-separating grooves of cutter ridges whichare adjacent in the circumferential direction are axially offset withrespect to each other. In order to create a tool which is characterisedby a long service life by the combined advantages of avibration-stabilised finishing cutter and a conventional roughingcutter, at least one circumferential cutting edge has an angle of twistwhich differs from the angle of twist of another circumferential cuttingedge. In addition, the chip-separating grooves of the circumferentialcutting edges which are equipped with a roughing profile in each casemerge into a preferably essentially flattened central section of theroughing profile by means of a predefined flank radius.

1. Shank cutter, which has a plurality of circumferential cutting edgeswhich run in a helical manner in the region of a cutting section of theshank cutter and of which at least one critical number are equipped ineach case with a roughing profile with chip-separating grooves withrounded bases, in such a manner that the chip-separating grooves ofcutter ridges which are adjacent in the circumferential direction areaxially offset with respect to each other, wherein at least onecircumferential cutting edge has an angle of twist which differs fromthe angle of twist of another circumferential cutting edge, and that thechip-separating grooves in each case merge into a central section of theroughing profile by means of a predefined flank radius.
 2. A shankcutter according to claim 1, wherein the angles of twist of adjacentcircumferential cutting edges are different.
 3. A shank cutter accordingto claim 1, wherein there are an even number of circumferential cuttingedges, of which in each case two lie diametrically opposite each otherand have the same angle of twist.
 4. A shank cutter according to claim1, wherein the pitch of the cutter is equal in a radial plane which liesin the region of the cutting section.
 5. A shank cutter according toclaim 1, wherein the angles of twist of the circumferential cuttingedges differ by 1° to 6°.
 6. A shank cutter according to claim 1,wherein the flank radius lies in the range from 0.1 to 1.0 mm.
 7. Ashank cutter according to claim 1, wherein the flank radius which ineach case faces away from the cutter shank is smaller than the otherflank radius of the chip-separating groove.
 8. A shank cutter accordingto claim 1, wherein the chip-separating grooves are angled towards aplane, which is perpendicular to a longitudinal axis of the shankcutter, of the shank cutter.
 9. A shank cutter according to claim 8,wherein the chip-separating grooves in each case follow in sections thecourse of a helix, the lead of which corresponds to the pitch of theroughing profile which is formed with the chip-separating groove.
 10. Ashank cutter according to claim 1, wherein the chip-separating groovesare parallel with a plane, which is perpendicular to a longitudinal axisof the shank cutter, of the shank cutter.
 11. A shank cutter accordingto claim 10, wherein the chip-separating grooves of cutter ridges whichare adjacent in the circumferential direction are axially offset withrespect to each other by the dimension V, where:V=T/n and T means the pitch of the roughing profile which is formed bythe chip-separating grooves and n means the number of circumferentialcutting edges.
 12. A shank cutter according to claim 1, wherein theflank radius is smaller than the smallest radius in the base of therounded chip-separating grooves.
 13. A shank cutter according to claim1, wherein the angles of twist are between 20 and 55°.
 14. A shankcutter according to claim 1, it wherein the shank cutter consists of ahard material, at least in the region of the cutting section.
 15. Ashank cutter according to claim 1, it wherein the shank cutter isprovided with a coating, at least in the region of the cutting section.16. A shank cutter according to claim 1, wherein the geometry of theroughing profile of the central section and/or the ratio of the pitch tothe depth of the chip-separating groove is selected as a function of thephysical properties of the material to be chipped.
 17. A shank cutteraccording to claim 1, wherein the roughing profile is essentiallyidentical in all the sectional planes which contain a longitudinal axisof the shank cutter.
 18. A shank cutter according to claim 1, whereinthe central section which lies between the chip-separating grooves has aconvexly curved surface.
 19. A shank cutter according to claim 18,wherein the radius of curvature of the central section is essentiallygreater than the flank radius.
 20. Use of a shank cutter according toclaim 1 for chipping with large cutting widths, in particular forcutting flanks, grooves, diagonal drill holes or spiral shapes.